The invention relates to a fastening element made from metal, for anchoring in a hole drilled in a building component, according to the preamble of claim 1.
DE 37 14 025 C2 discloses a fastening element of the same generic type having an expansion sleeve and an expansion member, the latter being axially displaceable on the shank of a threaded bolt. The threaded bolt has, at its forward end, an end-stop, which is in the form of a collar, and a helical spring, which is arranged between the end-stop and the axially displaceable expansion member. When a nut bearing against an article being fastened is screwed up on the threaded bolt, the latter is moved in the direction of the mouth of the drilled hole and, in the process, by means of the helical spring arranged between the end-stop and the displaceable expansion member, the expansion member is pressed into the expansion sleeve for anchoring of the latter in the hole drilled in the building component. At the same time, the helical spring is biased slightly so that, if the drilled hole widens as a result of crack formation, the expansion member is subjected to further pressing in order to compensate for the widening of the drilled hole. The known fastening element is, moreover, also capable of absorbing shock loads occurring, for example, as a result of an earthquake and consequently is capable of preventing the fastening element from coming out or the threaded bolt from breaking off.
In the case of the known solution it is, however, disadvantageous that, under certain circumstances, the further pressing of the expansion member into the expansion sleeve causes such an increase in the axial spacing between the expansion member and the end-stop that, afterwards, the helical spring is no longer biased and, under certain circumstances, even exhibits axial play. Because the expansion member is no longer braced and biased, further pressing of the expansion member is no longer possible in the event of further widening of the drilled hole resulting from enlargement of the crack, for example as a result of aftershocks.
The invention is accordingly based on the problem of providing a fastening element that is capable of absorbing a succession of shock loads without failure of the anchoring.
The solution to the problem is achieved by means of the features set but in claim 1.
As a result of using a sleeve-shaped spacing element, instead of a helical spring, and an end-stop in the form of an expander, the expander is, in the event of an overload acting on the threaded bolt, drawn into the spacing sleeve. As a result of the large amount of friction that is then caused on widening out and deformation of the spacing element, the spacing element is pressed against the expansion member, which is axially displaceable on the threaded bolt and which is consequently pushed further into the expansion sleeve. Because no restoring force is produced by the spacing element, the reduced spacing between the expander and the expansion member caused by the overload and, as a result, the biasing of the expansion member in the expansion sleeve are still present even after the loading has eased. In the event of further shock loads occurring, the expander is merely displaced inside the spacing element further towards the expansion member, the biasing pressure on the expansion member still being present by virtue of the friction inside the spacing element. The length of the spacing element consequently determines the length of the deformation zone, it being possible for the pull-through force to be adjusted by means of various parameters. It is, for example, possible for the spacing element to be in the form of a closed sleeve made from a soft metal or plastics material.
A preferred form of the spacing element is a spring sleeve having a longitudinal slit, the widening out of which spring sleeve is performed by the expander in the resilient region. It is advantageous for the expander to be in the form of a cone having a cylindrical collar adjacent thereto.
The fastening element according to the invention can be in the form of an undercut anchor, in which case the expansion sleeve is anchored in an undercut in the drilled hole, or in the form of a push-through anchor, in which case the shank of the threaded bolt, next to the region accommodating the expansion sleeve, widens out to the diameter of the expansion sleeve.